The present invention relates to a method of and device for adjusting the optical axis of an optical pick-up of an optical disk device to be normal to the recording/playback surface of the optical disk.
FIG. 22 to FIG. 25 shows a conventional optical disk device, and a device for adjusting the optical axis angle of the optical disk device. Referring to FIG. 22 to FIG. 25, reference numeral 10 denotes an optical disk having spiral or concentric tracks. Reference numeral 1 denotes a main base, 2a and 2b denote a pair of guide shafts fixed to the main base 1 and disposed at a distance from and in parallel with each other, 3 denotes an optical pick-up guided by the guide shafts 2a and 2b in the radial direction of the optical disk 10, and supported by the guide shafts 2a and 2b in such a manner that it can move in direction of the axes of the guide shafts. The signals recorded on the optical disk 10 are read by means of a reflected light resulting from a laser light via an objective lens 3a of the optical pick-up 3. Reference numeral 4 denotes a tangential-direction adjusting screw threaded through a protrusion 3b of the optical pick-up 3, and having an end abutting with one of the guide shafts, 2b. As shown in FIG. 24, when the screw 4 is turned, the optical pick-up 3 is rotated about the other the guide shaft 2a as shown by arrow A, and the optical axis angle of the optical pick-up 3 with respect to the optical disk 10 in the tangential direction is adjusted. Here, the xe2x80x9ctangential-direction optical axis anglexe2x80x9d means an angle of the optical axis of the optical pick-up 3 as seen in the direction of the guide shafts 2a, 2b (direction in which the guide shafts extend). When the optical axis angle is varied in this direction, the light spot formed by the optical pick-up 3 on the disk 10 is moved in the direction of a tangent on a track at a point confronting the optical pick-up 3.
Reference numeral 5 denotes a motor mounting member fixed to the base 1 by means of fixing screws 6a and 6b, and resiliently fixed by means of a radial-direction adjusting screw 7 extending through a hole in a part 5a of the mounting member 5 distant from the screws 6a and 6b, and threaded through the base 1. As shown in FIG. 25, when the radial-direction adjusting screw 7 is turned, the motor mounting member 5 is rotated about a line interconnecting the fixing screws 6a and 6b as shown by arrow B, for adjusting the radial-direction optical axis angle of the optical pick-up 3 with respect to the optical disk. Here, the radial-direction optical axis angle means an angle of the optical axis of the optical pick-up 3 as seen in direction normal to the axis of rotation of the turn table 9, and to the guide shafts 2a and 2b. When the optical angle is varied in this direction, the light spot formed by the optical pick-up 3 on the disk 10 is moved in the radial direction of the track, i.e., in the direction parallel with the guide shafts.
Reference numeral 8 denotes a disk motor fixed to the motor mounting member 5 by means of screws, not shown. Reference numeral 9 denotes a turn table fixed, by pressure insertion, to the disk motor 8.
The optical disk 10 is placed on the turn table 9, and information recorded thereon can be reproduced by means of the optical pick-up 3. Reference numeral 11 denotes a clamper for clamping the optical disk 10 in cooperation with the turn table 9. It is turned together with the turn table 9 and the optical disk 10 by means of the disk motor 8. Reference numeral 13 denotes an incident angle indicator connected to receive the output of the optical pick-up 3, via a playback amplifier (not shown) and indicating the incident angle (or a value corresponding thereto) of the optical axis of the optical pick-up 3 relative to the surface of the optical disk 10, which corresponds to the optical axis angle of the optical pick-up 3 with respect to the optical disk 10. Because the variation in the incident angle results in a time-axis variation, a jitter meter is used, of which the indication (indicated value) is the minimum when the incident angle of the optical pick-up 3 with respect to the optical disk 10 is zero.
The operations of the above arrangement at the time when signals are reproduced by means of the optical pick-up 3, and when the optical axis angle of the optical pick-up 3 with respect to the optical disk 10 is adjusted will next be described. The optical disk 10 which is clamped by the turn table 9 and the damper 11 is turned in a predetermined direction by means of the disk motor 8. The optical pick-up 3 is moved along the guide shafts 2a and 2b by a drive means (not shown), for continuous or intermittent reproduction from the region where the information is recorded on the optical disk 10. It is desirable that the optical axis of the laser light from the objective lens 3a of the optical pick-up 3 be normal to the optical disk 10, and the time-axis variation (hereinafter referred to as xe2x80x9cJitterxe2x80x9d) of the signal from the optical pick-up 3 is the minimum. If the optical axis angle is increased, and the jitter exceeds a certain value, skipping of sound, when sound is recorded on the optical disk, or noise in the image, when image is recorded on the optical disk, occurs. To prevent the skipping and noise, the optical pick-up 3 is rotated about the guide shaft 2a, for adjusting the tangential-direction optical axis angle of the optical pick-up 3 with respect to the optical disk 10 so that the indication at the incident angle indicator 13 is the minimum, and also, the motor mounting member 5 and the optical disk 10 mounted thereon are rotated about an axis (a line connecting the screws 6a and 6b) which is normal to the axis of rotation of the turn table 9 and the guide shafts 2a and 2b, by means of the radial-direction adjusting screw 7, for adjusting the radial-direction optical axis angle of the optical pick-up 3 with respect to the optical disk 10 so that the indication at the incident angle indicator 13 is the minimum.
The permissible range of the optical axis angle of the optical disk device differs from one system to another. In a system in which the recording density is low, combining parts of high mechanical precision may be sufficient, and there may be no need for the adjustment. In a system in which the recording density is high, however, the permissible range of the optical axis angle may be narrow, and optical axis angle adjustment is often required in either one or both of the radial and tangential directions, and an optical axis angle adjusting device with a high accuracy is desired.
The optical axis angle adjusting device for the optical disk device in the prior art makes adjustment of the optical axis angle of the optical pick-up 3 with respect to the optical disk 10 such that the jitter is the minimum. The dependency of jitter on the incident angle in the radial and tangential directions is such that it is substantially flat in the region near the optimum position, as shown in FIG. 26. Therefore, even if the incident angle of the image pick-up happen to be xcex8 i before the adjustment, the difference in the jitter compared with that in the optimum position is as small as J1, making it impossible to achieve accurate optical axis angle adjustment. As a result, during reproduction from the optical disk 10 with a surface undulation, jitter may be periodically increased with periodic variation in the incident angle due to the effect of the surface undulation, and sound skipping or image noise may be generated.
The invention has been made to solve the problems described above, and its object is to provide an optical axis angle adjusting method and device which enable high-precision adjustment of the optical axis angle of the optical pick-up 3 with respect to the optical disk 10, avoiding sound skipping and image noise during reproduction from an optical disk 10 with surface undulation.
According to the invention, there is provided a method of adjusting an optical axis angle in an optical disk device, comprising the steps of:
(a) placing an optical disk on a turn table such that the optical disk is inclined with respect to the turn table;
(b) causing rotation of the turn table on which said optical disk is placed;
(c) reading, by means of an optical pick-up, information signals recorded along a circumferentially-extending track on the optical disk which the disk is rotated, and producing adjustment signals based on the information signals read;
(d) detecting a first rotation phase of the disk and a second rotation phase of the disk which is 180 degrees apart from said first rotation phase,
an incident angle in a first direction of a light from said optical pick-up onto the disk being the maximum at one of said first and second rotation phase;
(e) indicating said adjustment signals outputted when the disk is at said first and second rotation phases; and
(f) adjusting the relative angle between the optical disk and the optical pick-up in said first direction, to thereby adjust said optical axis angle in said first direction;
whereby adjustment in said first direction is performed in said adjusting step (f) based on said indication at said step (e) such that the adjustment signals outputted when the disk is at said first and second rotation phases are at about the same level.
With the above arrangement, the optical axis angle can be adjusted easily and accurately.
The method may further comprises the step of:
(g) detecting a third rotation phase which is separated from the first rotation phase by 90 degrees of rotation of said disk, and a fourth rotation phase which is separated from the third rotation phase by 180 degrees of rotation of said disk;
(h) producing adjustment signals when the disk is at said third and fourth rotation phases based on the information signals read;
(i) indicating the adjustment signals when said disk is at said third and fourth rotation phases; and
(j) adjusting the relative angle between the optical disk and the optical pick-up in a second direction orthogonal to said first direction, to thereby adjust said optical axis angle in said second direction;
whereby adjustment in said second direction is performed in said adjusting step (j) based on said indication at said step (i) such that the adjustment signals outputted when the disk is at said third and fourth rotation phases are at about the same level.
With the above arrangement, the optical axis angle can be adjusted easily and accurately both in the first and second directions.
The adjustment signals may represent a time-axis variation of the information signals read by the optical pick-up.
With the above arrangement, the incident angle is detected based on the time axis variation (jitter) of the reproduced signal. Accordingly, it is not necessary to use a mechanical means for detecting the incident angle. Moreover, the incident angle can be detected on a real time basis. Accordingly, the adjustment can be achieved quickly.
The adjustment signals may represent an error rate of reproduced data obtained from the information signals read by the optical pick-up.
With the above arrangement, the incident angle is detected based on the error rate in the reproduced signal. Accordingly, it is not necessary to provide a mechanical means for detecting the incident angle. Moreover, the incident angle can be detected on a real time basis. Accordingly, the adjustment can be achieved quickly.
It may be so arranged that the optical pick-up is be moved in a radial direction of the disk so as to read from different radial positions on the disk, and the first direction is the radial direction.
It may be so arranged that the optical pick-up is moved in a radial direction of the disk so as to read from different radial positions on the disk, and said first direction is the radial direction, and said second direction is a tangential direction normal to the radial direction and to the axis of rotation of the disk.
According to another aspect of the invention, there is provided a device for adjusting an optical axis angle in an optical disk device, comprising:
means for placing an optical disk on a turn table such that the optical disk is inclined with respect to the turn table;
means for causing rotation of the turn table on which said optical disk is placed;
means, including an optical pick-up, for reading information recorded along a circumferentially-extending track on the optical disk which the disk is rotated, and producing adjustment signals based on the information read;
rotation phase detecting means for detecting a first rotation phase of the disk and a second rotation phase of the disk which is 180 degrees apart from said first rotation phase,
an incident angle in a first direction of a light from said optical pick-up onto the disk being the maximum at one of said first and second rotation phase;
means for indicating the adjustment signals outputted when the disk is at said first and second rotation phases; and
means for adjusting the relative angle between the optical disk and the optical pick-up in said first direction, to thereby adjust said optical axis angle in said first direction;
said device thereby enabling adjustment in said first direction by means of said adjusting means based on said indication by said indicating means such that the adjustment signals outputted when the disk is at said first and second rotation phases are at about the same level.
With the above arrangement, the optical axis angle can be adjusted easily and accurately.
It may be so arranged that said rotation phase detecting means also detects a third rotation phase which is separated from the first rotation phase by 90 degrees of rotation of said disk, and a fourth rotation phase which is separated from the third rotation phase by 180 degrees of rotation of said disk;
said generating means also generates the adjustment signals when the disk is at said third and fourth rotation phases;
said indicating means also indicates the adjustment signals when said disk is at said third and fourth rotation phases; and
said adjusting means also adjusts the relative angle between the optical disk and the optical pick-up in a second direction orthogonal to said first direction, to thereby adjust said optical axis angle in said second direction;
said disk thereby enabling adjustment in said second direction by means of said adjusting means based on said indication by said indicating means such that the adjustment signals outputted when the disk is at said third and fourth rotation phases are at about the same level.
With the above arrangement, the optical axis angle can be adjusted easily and accurately both in the radial and tangential directions.
It may be so arranged that the adjustment signals used for the adjustment of the optical axis angle of the disk represent a time-axis variation amount.
With the above arrangement, the incident angle is detected based on the time axis variation (jitter) of the reproduced signal. Accordingly, it is not necessary to provide a mechanical means for detecting the incident angle. Moreover, the incident angle can be detected on a real time basis. Accordingly, the adjustment can be achieved quickly.
It may be so arranged that the adjustment signals used for the adjustment of the optical axis angle of the disk represent an error rate of the playback data.
With the above arrangement, the incident angle is detected based on the error rate in the reproduced signal. Accordingly, it is not necessary to provide a mechanical means for detecting the incident angle. Moreover, the incident angle can be detected on a real time basis. Accordingly, the adjustment can be achieved quickly.
It may be so arranged that the optical pick-up is moved in a radial direction of the disk so as to read from different radial positions on the disk, and said first direction is the radial direction.
It may be so arranged that the optical pick-up is moved in a radial direction of the disk so as to read from different radial positions on the disk, and said first direction is the radial direction, and said second direction is a tangential direction normal to the radial direction and to the axis of rotation of the disk.